Choosing the right construction contract is an important part of planning a building project.
Whether you’re building a new home, duplex, commercial development, industrial building or undertaking a major renovation in NSW, the contract establishes the commercial relationship between the owner and builder and sets out important matters such as price, scope, payments, variations, timeframes and responsibilities.
For residential building work in NSW, there are also specific requirements under the Home Building Act 1989 (NSW) and associated legislation. The contract used must be appropriate for the type and value of work being undertaken.
At StoneyBark Certifiers, we do not prepare, recommend or provide legal advice about construction contracts. Our role as registered certifiers is separate and independent from the contractual relationship between an owner and builder.
This guide provides a general overview of common contracting models you may encounter in residential, commercial and larger construction projects.
What is a Construction Contract?
A construction contract is a legally binding agreement setting out the terms under which building or construction work will be performed.
Depending on the project and contract, it may address matters including:
- Scope of building work
- Plans and specifications
- Contract price
- Progress payments
- Project commencement and completion
- Responsibilities of the parties
- Variations
- Extensions of time
- Prime cost and provisional sum items
- Insurance requirements
- Defects
- Dispute resolution
- Suspension or termination
- Other project-specific conditions
For homeowners in NSW, residential building contracts are subject to specific consumer protection requirements.
For this reason, it is important to use an appropriate contract and obtain professional or legal advice before signing.
Why Does the Construction Contract Matter?
Construction projects can involve significant financial commitments and many different parties.
A properly prepared contract can help establish:
- What work the builder has agreed to complete
- What the owner has agreed to pay
- When payments become due
- How changes to the work are handled
- Who is responsible for particular matters
- How delays and extensions of time are managed
- How disputes are dealt with
- What happens if either party does not meet their obligations
However, signing a construction contract does not replace the need for development approvals, building certification or other regulatory requirements.
The contractual relationship between an owner and builder is separate from the statutory certification process.
1. Lump Sum or Fixed Price Contract
A Lump Sum Contract, often referred to as a Fixed Price Contract, establishes an agreed contract price for a defined scope of construction work.
It is one of the commonly encountered contracting models in residential construction.
May Be Used For
- New homes
- Duplexes
- Townhouses
- Alterations and additions
- Defined residential projects
- Certain commercial projects
Potential Advantages
- Greater initial price certainty
- Defined scope of work
- Easier budgeting
- Clear basis for progress payments
Important Considerations
“Fixed price” does not necessarily mean the final amount paid can never change.
The contract price may change because of matters such as:
- Approved variations
- Prime cost items
- Provisional sums
- Site conditions
- Changes requested by the owner
- Other adjustments permitted under the contract
Owners should understand exactly what is included and excluded before signing.
2. Cost Plus Contract
IUnder a Cost Plus Contract, the owner generally pays the actual cost of carrying out the work plus an agreed builder’s fee or margin.
This model may be considered where the final scope or cost of the work is difficult to determine accurately before construction.
May Be Considered For
- Complex renovations
- Certain heritage projects
- Projects involving uncertain existing conditions
- Highly customised construction
Potential Advantages
- Greater flexibility where the scope may change
- Actual project costs can be tracked
- May accommodate uncertain construction conditions
Important Considerations
- Final cost may be difficult to predict
- Detailed records are important
- The method for calculating the builder’s margin should be clearly understood
- Cost monitoring becomes particularly important
Important: Cost plus contracting for residential building work in NSW is subject to legal requirements. Appropriate legal advice should be obtained before entering into this type of agreement.
3. Time and Materials Contract
A Time and Materials Contract generally calculates payment based on the labour time and materials used to complete the work.
Rather than agreeing on one total price for the entire project, charges are based on agreed rates and actual resources used.
May Be Used For
- Maintenance work
- Repairs
- Smaller construction works
- Work where the exact scope is difficult to determine initially
- Certain specialist trade work
Potential Advantages
- Flexible where the scope is uncertain
- Changes can potentially be accommodated more easily
- Suitable for some smaller or evolving scopes of work
Important Considerations
- Final cost may be uncertain
- Labour and material records should be maintained
- Rates and mark-ups should be clearly documented
- Appropriate contractual and legislative requirements still apply
For NSW residential building work, specific contracting requirements may apply depending on the nature and value of the work.
4. Unit Price Contract
A Unit Price Contract calculates payment according to measured quantities of completed work.
For example, pricing might be based on:
- Square metres
- Cubic metres
- Linear metres
- Tonnes
- Individual units
This type of arrangement is more commonly encountered in civil, infrastructure and large-scale construction than standard residential home building.
Common Applications
- Civil construction
- Earthworks
- Road construction
- Infrastructure
- Excavation
- Large subdivisions
- Repetitive construction activities
Potential Advantages
- Useful where exact quantities are uncertain at tender stage
- Provides agreed rates for individual units of work
- Can provide transparent measurement of completed work
Important Considerations
The final project price can increase or decrease depending on the actual quantities completed.
Accurate measurement and documentation are therefore important.
5. Guaranteed Maximum Price (GMP) Contract
A Guaranteed Maximum Price, or GMP, arrangement establishes a maximum contract amount, subject to the particular terms of the agreement.
It is more commonly associated with larger commercial or sophisticated construction projects.
May Be Used For
- Commercial developments
- Larger residential developments
- Institutional projects
- Major construction projects
Potential Advantages
- Provides an agreed upper cost framework
- Can encourage active cost management
- May provide greater budget certainty than some open-ended arrangements
Important Considerations
A GMP should not automatically be interpreted as an absolute guarantee that the owner can never pay more.
Variations, scope changes, exclusions, unforeseen circumstances and other contractual provisions may affect the final amount.
The particular contract terms are therefore critical.
6. Design and Construct Contract
Under a Design and Construct (D&C) Contract, one contracting party generally takes responsibility for both the design and construction components of the project.
Rather than the owner separately engaging a designer and builder under completely separate arrangements, the design and construction responsibilities are brought together under the contractual structure.
Common Applications
- Commercial developments
- Industrial buildings
- Apartments
- Larger residential developments
- Institutional projects
Potential Advantages
- Single contractual point of responsibility
- Greater coordination between design and construction
- Potential efficiencies in project delivery
- Construction considerations can be incorporated during design
Important Considerations
The contract should clearly define:
- Design responsibility
- Performance requirements
- Scope
- Approval responsibilities
- Documentation requirements
- Design changes
- Construction obligations
Importantly, contractual responsibility for design does not remove the need to obtain required development approvals and certification.
7. Construction Management Contract
For larger or more complex projects, a Construction Management model may be used.
Under this type of arrangement, a construction manager coordinates aspects of the construction process, while individual trade packages may be contracted separately depending on the contractual structure.
May Be Used For
- Large commercial projects
- Complex developments
- Projects requiring early construction involvement
- Projects with multiple specialist trade packages
Potential Advantages
- Early involvement of construction expertise
- Flexibility during design and procurement
- Ability to package different components of the work
Important Considerations
This model can involve a more complex allocation of responsibility and risk than a conventional fixed-price building contract.
Clear contractual documentation and professional advice are particularly important.lthcare and institutional buildings.
8. Subcontractor Contracts
Most construction projects involve specialist subcontractors.
Depending on the project, these may include:
- Electricians
- Plumbers
- Carpenters
- Concreters
- Roofers
- Waterproofers
- Bricklayers
- Plasterers
- Painters
- Landscapers
- Fire safety contractors
A subcontract generally establishes the contractual relationship between the head contractor and the subcontractor for a defined portion of the work.
It may address:
- Scope of work
- Price
- Payment
- Program and deadlines
- Workmanship
- Insurance
- Safety requirements
- Variations
- Defects
- Compliance obligations
A subcontract is generally separate from the main contract between the property owner and head contractor.
9. Incentive-Based Construction Contract
An Incentive Contract incorporates financial or other incentives linked to agreed project outcomes.
Depending on the contract, incentives might relate to:
- Early completion
- Cost performance
- Quality targets
- Safety outcomes
- Project milestones
- Other measurable performance objectives
These arrangements are more commonly found on larger commercial, infrastructure and sophisticated construction projects than ordinary residential building projects.
Potential Advantages
Incentives can help align commercial objectives between project participants.
Important Considerations
Performance targets must be clearly defined and objectively measurable.
The contract should also clearly explain how incentives, bonuses or other adjustments are calculated.
What About Integrated Project Delivery?
Integrated Project Delivery (IPD) is another collaborative project delivery model sometimes discussed in the construction industry.
Rather than treating it as one of the nine primary contract types in this guide, it is better understood as a collaborative approach involving key project participants—such as the owner, designer and contractor—working together from an early stage.
IPD is more commonly associated with sophisticated and complex projects.
Residential Building Contracts in NSW
Homeowners undertaking residential building work in NSW should be particularly careful about contractual requirements.
NSW legislation imposes requirements on contracts for certain residential building work.
Depending on the type and value of the work, requirements can relate to matters such as:
- Written contracts
- Required contract information
- Deposits
- Progress payments
- Variations
- Statutory warranties
- Insurance
- Consumer rights
For residential building work valued above the applicable threshold, Home Building Compensation cover may also be required before certain payments are taken or work commences, subject to the applicable legislation and exemptions.
Because these requirements can change and depend on the circumstances, owners and builders should check the current requirements with NSW Fair Trading and obtain appropriate professional advice.
Construction Contracts vs Building Certification
It is important to understand the distinction between a construction contract and building certification.
The construction contract governs the commercial and legal relationship between parties such as the owner and builder.
Building certification is a separate statutory process.
At StoneyBark Certifiers, we do not:
- Prepare construction contracts
- Provide legal advice about contracts
- Determine contractual disputes
- Administer payments between owners and builders
- Supervise the builder’s work
- Act as the owner’s project manager
Our role as registered certifiers is independent.
Depending on the project, our certification services may include:
- Complying Development Certificate assessment
- Construction Certificate assessment
- Principal Certifier services
- Required critical stage inspections
- Occupation Certificate assessment
- Other certification services within our scope of registration
This distinction is important because appointing a Principal Certifier does not transfer responsibility for managing the construction project to the certifier.
Does the Building Contract Need to Match the Approved Plans?
The contract documents, approved plans and construction documentation should be carefully coordinated before work begins.
If the owner decides to change the building during construction, the change may involve more than simply agreeing on a contractual variation with the builder.
Depending on the nature of the proposed change, it may also affect the development approval or construction certificate.
This means a contractual variation does not automatically authorise a change to approved building work.
Before carrying out changes that differ from approved plans, the relevant approval and certification implications should be considered.
Choosing the Right Construction Contract
There is no single construction contract that is best for every project.
The appropriate contractual arrangement depends on factors including:
- Type of development
- Project value
- Complexity
- Certainty of scope
- Budget
- Design responsibility
- Construction timeframe
- Allocation of risk
- Likelihood of variations
- Procurement method
- Relationship between project participants
A relatively straightforward new home may require a very different contractual structure from a major commercial or industrial development.
Before entering into a construction contract, consider obtaining advice from an appropriately qualified construction lawyer or other relevant professional.
Questions to Ask Before Signing a Building Contract
Before signing, owners should make sure they understand key issues such as:
- What exactly is included in the contract price?
- What has been excluded?
- Are there prime cost or provisional sum items?
- How are variations approved and priced?
- What are the progress payment stages?
- What happens if construction is delayed?
- Who is responsible for obtaining approvals?
- What insurance is required?
- How are defects handled?
- How are disputes resolved?
- Are the plans and specifications attached to the contract the correct versions?
- What circumstances allow either party to terminate the contract?
For a major financial commitment, independent legal review before signing can be valuable.
Why Choose StoneyBark Certifiers?
While StoneyBark Certifiers does not advise on which construction contract you should enter into, we provide professional building certification services for eligible developments across Sydney and NSW.
Our focus is on:
- Independent building certification
- Clear communication
- CDC assessment
- Construction Certificate assessment
- Principal Certifier services
- Required critical stage inspections
- Occupation Certificate assessment
- Professional and responsive certification services
We work with homeowners, builders, architects, designers and developers throughout relevant stages of the certification process.
Frequently Asked Questions
What Is the Most Common Construction Contract for a New Home?
Fixed-price or lump-sum arrangements are commonly encountered in residential construction. However, the appropriate contract depends on the project and applicable NSW residential building requirements.
Does a Fixed-Price Contract Mean My Price Cannot Change?
Not necessarily.
The final amount can potentially change because of approved variations, prime cost items, provisional sums and other adjustments permitted under the particular contract.
What Is the Difference Between Fixed Price and Cost Plus?
A fixed-price contract establishes an agreed price for a defined scope, subject to the contract terms.
Under a cost-plus arrangement, the owner generally pays actual construction costs plus an agreed fee or margin.
Can I Change My Design After Signing the Building Contract?
Potentially, but the contractual variation is only one consideration.
If the proposed change affects approved building work, you may also need to address development approval and certification requirements before carrying out the changed work.
Does StoneyBark Certifiers Prepare Building Contracts?
No.
StoneyBark Certifiers provides independent building certification services. We do not prepare building contracts or provide legal advice regarding contractual arrangements between owners, builders or subcontractors.
Does My Principal Certifier Supervise My Builder?
No.
The Principal Certifier performs an independent statutory certification role. The Principal Certifier is not the builder, site supervisor or project manager.
Do I Need a Building Contract Before Getting a CDC or Construction Certificate?
The documentation and contractual requirements depend on the type of project and applicable NSW legislation. Building approval, certification and residential building contract requirements are related aspects of a project but perform different legal functions.
Should I Have My Construction Contract Reviewed Before Signing?
For a significant construction project, obtaining independent legal advice can help you understand your obligations, risks and rights before entering into the contract.
Planning a Construction Project in Sydney or NSW?
A clear construction contract is important—but so is ensuring that the required building approvals, certification and inspections are correctly addressed.
If you’re planning a new home, duplex, granny flat, renovation, commercial building or other development, StoneyBark Certifiers can assist with certification services for eligible projects.
Our Certification Services
CDC Assessments • Construction Certificates • Principal Certifier Services • Critical Stage Inspections • Occupation Certificate Assessments
Ready to Discuss Your Project?
Send us your plans and project information to request a certification fee proposal.
This article provides general information only and is not legal, contractual, financial or project-management advice. Construction contract requirements depend on the type and value of work, the parties involved and applicable legislation. Obtain independent legal and professional advice relevant to your circumstances before entering into a construction contract.
